An inflatable vehicle occupant protection device, such as an air bag, is inflated upon the occurrence of a vehicle crash. The air bag is part of a vehicle occupant protection apparatus which further includes a crash sensor and an inflator. The crash sensor senses vehicle conditions that indicate the occurrence of a crash. When the crash sensor senses a crash-indicating condition of at least a predetermined threshold level, the inflator is actuated. The inflator then emits inflation fluid which inflates the air bag into the vehicle occupant compartment. When the air bag is inflated in this manner, it engages an occupant of the vehicle to help protect the occupant from a forceful impact with parts of the vehicle as a result of the crash.
The manner in which the air bag engages the vehicle occupant can be influenced by factors such as the force with which the occupant moves against the air bag and the pressure of the inflation fluid in the air bag. Those factors, in turn, can be influenced by various conditions that exist at the time of the crash. Such crash conditions may include deceleration or other vehicle conditions, and/or vehicle occupant conditions such as the weight and position of the occupant.